The present invention relates to a photocatalyst-supporting body for conversion and removal of organic or inorganic substances in a fluid (gas or liquid) stream by using a semiconductor photocatalyst, and an apparatus utilizing the photocatalyst-supporting body.
Ever increasing use of petrochemicals has caused serious complex pollution or contamination of living environment by noxious substances. To avoid the pollution and contamination problems, a fluid purification method utilizing a photocatalyzed oxidative decomposition of pollutants and contaminants by a semiconductor photocatalyst has been proposed.
For example, an apparatus or instrument having as a part thereof a substrate supporting a semiconductor photocatalyst is placed in a flow path of a fluid stream containing noxious inorganic or organic substances so as to bring the noxious substances into contact with the semiconductor photocatalyst thereby to decompose the noxious substances. To enhance the photocatalytic efficiency, it is needed to increase the photocatalytic surface area and to sufficiently activate the semiconductor photocatalyst with an electromagnetic wave having a wavelength capable of activating the photocatalyst.
Several proposals have been made on the method of increasing the area of the photocatalytic surface and the method of forming a photocatalyst layer. Japanese Patent Laid-Open No. 5-309267 discloses a photocatalyst-supporting body comprising a substrate made of ceramics, glass, metals and plastics and a photocatalyst powder bound to the substrate by a metal oxide derived from a corresponding metal oxide sol. Japanese Patent Laid-Open No. 8-196903 discloses a photocatalyst-supporting body comprising a porous substrate made of ceramics, glass and metal, and a titanium oxide layer with fine pores. However, although the photocatalytic surface area is increased, the proposed photocatalyst-supporting bodies are still insufficient in activating the semiconductor photocatalyst by electromagnetic wave and providing a sufficient contact of a fluid stream with the semiconductor photocatalyst.
Japanese Patent Laid-Open No. 8-246192 discloses a photocatalyst-supporting body comprising a titanium or titanium alloy plate and an oxide layer containing anatase titanium oxide. However, the titanium or titanium alloy plate is very expensive and rigid to have a poor formability. Japanese Patent Laid-Open No. 9-206537 discloses a drying device capable of decomposing food oil to carbon dioxide and water, in which the photocatalyst is coated on a filter made of a punching metal.
To mount a photocatalyst-supporting body into an apparatus or instrument as a part thereof, the substrate supporting the semiconductor photocatalyst is preferred to be easily worked by press working, etc., and preferred to have a good flexibility to ensure easy bending and folding. However, the substrates, in particular those made of inorganic materials conventionally used have been poor in workability and flexibility thereby to limit the field to which the photocatalyst-supporting body is applied.
Japanese Patent Laid-Open No. 8-215577 discloses to support the photocatalyst on a meshed structure having an opening of 0.5 mm or smaller to improve the formability of the photocatalyst-supporting body. The meshed structure is made of metal, metal oxide, plastic or natural fiber. However, since the photocatalyst is coated directly on the meshed substrate, the photocatalytic surface area is small thereby failing to exhibit a sufficient photocatalytic efficiency.
Accordingly, an object of the present invention is to provide a photocatalyst-supporting body comprising a substrate and a photocatalyst disposed thereon, in which the surface area of the substrate is increased to ensure a uniform activation of the semiconductor photocatalyst and an enhanced contact of a fluid stream with the semiconductor photocatalyst. The present invention also provides a photocatalyst apparatus utilizing such a photocatalyst-supporting body.
As a result of the intense research in view of the above objects, the inventors have found that the problems in the prior art can be solved by coating the surface of the substrate with particles in layer so that the particles are coated densely on the substrate and coated roughly with increasing distance from the substrate in the thickness direction or vice versa, fixing the coated particles on the substrate, and then supporting the photocatalyst on the fixed particles. The coated particles increase the surface of the substrate, and as a result thereof, increase the area of photocatalytic surface.
The inventors have further found that the above problems can be eliminated by supporting the photocatalyst on a porous layer, which is made of a non-woven wire fabric or metal particles, fixedly disposed on a substrate of a meshed structure.
Thus, in a first aspect of the present invention, there is provided a photocatalyst-supporting body comprising a substrate, a particle layer fixedly disposed on at least one surface of the substrate, and a semiconductor photocatalyst layer deposited on the surface of the particles of the particle layer, the particle layer either being roughly formed in the vicinity of the surface of the substrate and densely formed with increasing distance from the surface of the substrate or being densely formed in the vicinity of the surface of the substrate and roughly formed with increasing distance from the surface of the substrate in the thickness direction of the particle layer to increase the surface area of the substrate.
The particles of the particle layer, the particle layer either being roughly formed in the vicinity of the surface of the substrate and densely formed with increasing distance from the surface of the substrate or being roughly formed in the vicinity of the surface of the substrate and densely formed with increasing distance from the surface of the substrate in the thickness direction of the particle layer to.
In a second aspect of the present invention, there is provided a photocatalyst-supporting body comprising: (1) a substrate of a meshed structure made of a metallic material selected from the group consisting of stainless steel, aluminum, an aluminum alloy, titanium, a titanium alloy, copper and a copper alloy, the substrate being in the form of a flat plate or three-dimensional structure; (2) a porous layer securely disposed on at least one surface of the substrate, the porous layer being a nonwoven metal fabric or sintered metal particles, each made of a metallic material selected from the group consisting of stainless steel, aluminum, an aluminum alloy, titanium, a titanium alloy, copper and a copper alloy; and (3) a photocatalyst layer deposited on the porous layer.
In a third aspect of the present invention, there is provided a photocatalytic apparatus comprising: (1) a photocatalyst-supporting body, as defined above, having a flat plate shape; and (2) a pair of light sources for illuminating the photocatalyst-supporting body with light having a wavelength capable of activating a photocatalyst, pair of light sources being respectively disposed along the opposite sides of the photocatalyst-supporting body so that one of the light sources illuminates a front surface of the photocatalyst-supporting body and the other illuminates a back surface of the photocatalyst-supporting body.